What’s the difference between greenies dental treats and any standard hard food like science diet or royal canin?

I have been giving my cats greenies twice a day for years now and someone told me that the dental benefit the cats get is from the hard texture of the treats scraping plaque off their teeth. If that’s the case, what’s the difference between giving them greenies and any other hard food? Could I have just been doing that the whole time and saving money?